NCERT Solutions For Class 10 Science Chapter-3 Metals And Non-Metals
1.Give an example of a metal which
(i) is a liquid at room temperature.
(ii) can be easily cut with a knife.
(iii) is the best conductor of heat.
(iv) is a poor conductor of heat.
(i) Metal that exists in liquid state at room temperature is mercury.
(ii) Metal that can be easily cut with a knife is sodium.
(in) Metal that is the best conductor of heat is silver.
(iv) Metal that is a poor conductor of heat is lead.
2.Explain the meanings of malleable and ductile.
Answer.Malleable: Substances that can be beaten into thin sheets are called malleable. Most of the metals are malleable. The most malleable metals are gold and silver.
Ductile: Substances that can be drawn into thin wires are called ductile. Most of the metals are ductile. Platinum, gold and silver are the most ductile metals.
1.Why is sodium kept immersed in kerosene oil?
Answer. Sodium is a very reactive metal and combines explosively with air(oxygen) at room temperature. It also reacts violently with cold water. Hence, it catches fire if kept in open. Therefore, to prevent accidental fires and accidents, sodium is stored immersed in kerosene oil.
2.Write equations for the reactions of
(i) iron with steam.
(ii) calcium and potassium with water.
(i) 3Fe(s) + 4H2O(l)—–> Fe3O4(s) + 4H2(g)
(ii) Ca(s) + 2H2O(Z)—–> Ca(OH)2(ag) + H2(g) + Heat
2K(s) + 2H2O (Z)—–> 2KOH(aq) + H2(g) + Heat
3. Samples of four metals A, B, C and D were taken and added to the following solutions one by one. The results obtained have been tabulated as follows.
Use the Table above to answer the following questions about metals A, B, C and D.
(i) Which is the most reactive metal?
(ii) What would you observe if B is added to a solution of copper (II) sulphate?
(iii) Arrange the metals A, B, C and D in the order of decreasing reactivity.
A + Fe SO4 –> No reaction, i.e. A is less reactive than iron.
A + CuSO4–> Displacement, i.e. A is more reactive than copper.
B + FeSO4 –> Displacement, i.e. B is more reactive than iron.
B + ZnSO4 –> No reaction, i.e. B is less reactive than zinc.
C + FeSO4 –> No reaction, i.e. C is less reactive than iron.
C + CuSO4 –> No reaction, i.e. C is less reactive than copper.
C + ZnSO4 –> No reaction, i.e. C is less reactive than zinc.
C + AgNO3 –> Displacement, i.e. C is more reactive than silver.
D 4- FeSO4/CuSO4/ZnSO4/AgNO3 –> No reaction, i.e.
D is less reactive than iron, copper, zinc, and silver.
From the above equations, conclude:
(i) B is the most reactive metal.
(ii)If B is added to a solution of copper (II) sulphate, then it would displace copper.
B + CuSO4 —-> Displacement
(iii) The arrangement of the metals in the order of decreasing reactivity is: B > A > C > D
4.Which gas is produced when dilute hydrochloric acid is added to a reactive metal? Write the chemical reaction when iron reacts with dilute H2SO4.
Answer. When dilute hydrochloric acid is added to a reactive metal, hydrogen gas is evolved.
The reaction between iron and H2S04 is:
Fe(s) + H2SO4(dil.)—-> FeSO4(aq) + H2(g)
5.What would you observe when zinc is added to a solution of iron(II) sulphate? Write the chemical reaction that takes place.
Answer. Zinc is more reactive than iron. Therefore, if zinc is added to a solution of iron (II) sulphate, then it would displace iron from the solution.
Zn(s) + FeSO4(aq)—-> ZnSO4(aq) + Fe(s)
1.(i) Write the electron-dot structures for sodium, oxygen and magnesium.
(ii) Show the formation of Na2O and MgO by the transfer of electrons.
(iii) What are the ions present in these compounds?
Answer.(i) Electronic configuration of sodium is 2,8,1.
Electron dot structure of sodium is: Na.
Electronic configuration of oxygen is 2,6.
Electron dot structure of oxygen is:
Electronic configuration of magnesium is 2,8,2.
Electron dot structure of magnesium is: Mg:
(a) Formation of Na2O
(b) Formation of MgO
(iii) The ions present are Na+, O2- and Mg2+.
2.Why do ionic compounds have high melting points?
Answer. Ionic compounds have high melting points because of the strong force of attraction between the oppositely charged ions. High energy is required to break the metallic bonds between these ions.
1.Define the following terms.
(i) Mineral (ii) Ore (iii) Gangue
(i) A naturally occurring inorganic material formed through geological processes is known as a mineral.
(ii)The minerals from which metals can be extracted conveniently and profitably is known as an ore.
(iii) The unwanted material present in the ores is called gangue.
2.Name two metals which are found in nature in the free state.
Answer.The metals present at the bottom of the reactivity series are mostly found in free state. For example: gold, silver, and platinum.
3.What chemical process is used for obtaining a metal from its oxide?
Answer. The chemical process used for obtaining a metal from its oxide is reduction. There are mainly three different methods of reduction:
(i) By heating
(ii)By using carbon
(iii)By using aluminium, calcium, sodium etc. as reducing agents.
1.Metallic oxides of zinc, magnesium and copper were heated with the following metals.
Answer. In which cases will you find displacement reactions taking place?
2, Which metals do not corrode easily?
Answer. Gold, platinum, rhodium.
3. What are alloys?
Answer. A homogeneous mixture of two or more metals or a metal and a non-metal is known as an alloy. For example, brass is an alloy of copper and zinc.
1.Which of the following pairs will give displacement reactions?
(a) NaCl solution and copper metal
(b) MgCl2 solution and aluminium metal
(c) FeS04 solution and silver metal
(d) AgNOg solution and copper metal.
(d) Cu(s) + 2AgNO3(aq)—> Cu( NO3)2(aq) + 2Ag(s)
because copper is more reactive than Ag.
2.Which of the following methods is suitable for preventing an iron frying pan from rusting?
(a) Applying greese (b) Applying paint
(c) Applying a coating of zinc (d) All of the above.
Answer. (c) Greese and paints are organic matter which can burn on heating. So, we do not apply greese or paint on a frying pan to prevent it from rusting. We can prevent it from rusting by applying coating of zinc. Zinc is more reactive than iron and hence it does not allow iron to rust.
3.An element reacts with oxygen to give a comppund with a high melting point. This compound is also soluble in water. The element is likely to be
(a) calcium. (b) carbon.
(c) silicon. (d) iron.
Answer. (a) Calcium oxide has high melting point as it is ionic in nature and is soluble in water.
4.Food cans are coated with tin and not with zinc because
(a) Zinc is costlier than tin.
(b) Zinc has a higher melting point than tin.
(c) Zinc is more reactive than tin.
(id) Zinc is less reactive than tin.
Answer. (c) Zinc is more reactive than tin, that is why, tin is used.
5.You are given a hammer, a battery, a bulb, wires and a switch.
(a) How would you use them to distinguish between samples of metals and non-metals?
(b) Assess the usefulness of these tests in distinguishing between metals and non-metals.
- Take the sample of metal.
Hammer it for long time. Observe the metal after sometime.
- Take the sample of non-metal and hammer it a little.
You will observe that metal changes into sheets on hammering, i.e. it is malleable whereas non-metal is brittle and it breaks on hammering.
- Set the apparatus as shown in the figure above. Take the sample of metal and put it between the clips. Switch on the current and observe the bulb. Now take the sample of non-metal and insert it between clips. Switch on the current and observe the bulb.
You will observe that the bulb glows when current is switched on in case of metal sample.xThe bulb does not glow in case of non-metal sample. This shows metals are good conductors of electricity whereas non-metals are bad conductors of electricity.
(b) These two tests can be used to distinguish between metals and non-metals. Hammering can be used in most of metals except in case of sodium, potassium and lithium.
Conduction of electricity can be used in classification of most of the metals and non-metals except in graphite which is a non-metallic conductor.
6.What are amphoteric oxides? Give two examples of amphoteric oxides.
Answer. Those oxides which act as both acidic as well as basic are called amphoteric oxides, e.g. Al2 O3 s and ZnO are amphoteric oxides.
7.Name two metals which will displace hydrogen from dilute acids and two metals which will not.
Answer. Zn and A1 will displace hydrogen from dilute acids because they are more reactive than hydrogen whereas Cu and Ag cannot displace hydrogen from dilute acids because they are less reactive than hydrogen.
Zn(s) + 2HCl(dil)—> ZnCl2 (aq) + H2 (g)
2Al(s) + 6HCl (dil)—> 2AlCl3(aq) + 3H2(g)
8.In the electrolytic refining of a metal M, what would you take as the anode, cathode and electrolyte?
Answer.Impure metal acts as anode, pure metal acts as cathode. Soluble salt of metal acts as electrolyte.
9.Pratyush took sulphur powder on a spatula and heated it. He collected the gas evolved by inverting a test tube over it as shown in the given figure.
(a) What will be the action of gas on
(i) dry litmus paper?
(ii) moist litmus paper?
(b) Write a balanced chemical equation for the reaction taking place.
(a) (i) There will be no effect of gas on dry litmus paper.
(ii) Moist blue litmus paper will turn red.
(b) S(s) + O2(g) —> SO2(g)
Sulphur Oxygen Sulphur dioxide
SO2(g) + H20 (l) —> H2SO3(aq)
Sulphurous acid turns blue litmus red.
10. State two ways to prevent the rusting of iron.
Answer. (i) Painting: Iron articles are painted so that surface does not come in contact with air and water and it does not get rusted.
(ii) Galvanisation: It is a process in which iron articles are coated with zinc metal so as to prevent them from rusting. Zinc is more reactive than iron, therefore, it loses electrons more readily and prevents iron from rusting.
11.What type of oxides are formed when non-metals combine with oxygen?
Answer. Mostly acidic oxides are formed when non-metal combines with oxygen.
12. Give reasons.
(i) Platinum, gold and silver are used to make jewellery.
(ii) Sodium, potassium and lithium are stored under oil.
(iii) Aluminium is a highly reactive metal, yet it is used to make utensils for cooking.
(iv) Carbonate and sulphide ores are usually converted into oxides during the process of extraction.
(i) It is because they are highly lustrous and least reactive.
(ii)They are highly reactive. They catch fire and start burning when kept open in the air. To prevent their reaction with oxygen, moisture and carbon dioxide of air, they are stored under oil.
(iii) It is because aluminium is a good conductor of heat.
(iv) It is because it is easier to reduce oxide ores as compared to carbonates and sulphides.
13. You must have seen tarnished copper vessels being cleaned with lemon or tamarind juice. Explain why these sour substances are effective in cleaning the vessels.
Answer. It is because basic copper carbonate formed on copper vessel reacts with acid present in lemon or tamarind juice and gets dissolved and green layer is removed. ‘
14. Differentiate between metal and non-metal on the basis of their chemical properties.
15. A man went door to door posing as a goldsmith. He promised to bring back the glitter of old and dull gold ornaments. An unsuspecting lady gave a set of gold bangles to him which he dipped in a particular solution. The bangles sparkled like new but their weight was reduced drastically. The lady was upset but after a futile argument the man beat a hasty retreat. Can you play the detective to find out the nature of the solution he had used?
Answer. The solution he had used was aqua regia, which is a freshly prepared mixture of concentrated hydrochloric acid and concentrated nitric acid in the ratio 3:1. Aqua regia is one of the few reagents that is able to dissolve gold. When the person claimed to be goldsmith dipped bangles in aqua regia, some of the gold got dissolved and hence weight of the bangles got reduced.
16. Give the reason why copper is used to make hot water tanks and not steel (an alloy of iron).
Answer. Copper is better conductor of heat than steel therefore, it is used for making hot water tanks.